1. Field of the Invention
The present invention relates to a patterning method and a computer readable medium therefor in a direct patterning apparatus (the apparatus that performs patterning without using a mask) which forms a desired pattern on a surface of an object (patterning target) by exposing the surface of the object to light by using a plurality of spatial light modulation elements installed and assigned to respective exposure areas defined along a relative moving direction of the object.
2. Description of the Related Art
A direct patterning apparatus for exposing an object by using spatial light modulation elements such as a digital micromirror device (DMD), that is, a maskless exposure apparatus performs an exposure process to form a pattern on the surface of an object substrate by moving the object substrate relatively in one direction with respect to the patterning apparatus at a regular transfer speed while changing the pattern being output from the spatial light modulation elements in accordance with the relative movement, in order to continuously expose the object substrate (object) having a large patterning area (for example, see JP-A-2005-300805 for reference). In this case, an area on which one spatial light modulation element can perform the patterning at one time in a direction perpendicular to the relative moving direction (transfer direction) of the object substrate is limited. Thus, the plurality of spatial light modulation elements are aligned in the direction perpendicular to the transfer direction of the object substrate, so that the direct patterning apparatus can evenly perform the patterning on the object in that direction.
When directly exposing a resist formed on the object substrate, the maskless exposure apparatus using the digital micromirror device creates pattern data corresponding to patterns for exposure, inputs the pattern data to the digital micromirror device, and moves each of a plurality of micromirrors in the digital micromirror device in a tilted manner in accordance with the pattern data. In this manner, the maskless exposure apparatus forms exposure patterns corresponding to the pattern data, by appropriately changing a direction of reflected light coming from each micromirror obtained by projecting light onto the digital micromirror device, and exposing the resist on the object substrate to the light (for example, see JP-A-10-112579 for reference).
The micromirrors of the digital micromirror device are aligned two-dimensionally, so that the alignment direction of each column is perpendicular to that of each row (for example, see JP-A-2004-009595 for reference). It is possible to perform the exposure process with more minute resolution than a pitch between the micromirrors of the digital micromirror device, by tilting the micromirror rows (or columns) of the digital micromirror device mounted on a patterning head for a predetermined angle with respect to the relative moving direction of the object substrate (that is, a scanning direction of a stage on which the object substrate is mounted). In this case, the tilting angle of the micromirrors of the digital micromirror device is appropriately determined, so that one point on the surface of the object substrate is exposed to light for a plurality of times by the plurality of micromirrors positioned apart from each other at an approximately regular interval on the scanning lines. A non-uniform irradiance in the digital micromirror device and a non-uniform irradiance between different digital micromirror devices can be suppressed by the multiple exposure by the plurality of micromirrors.
In the direct patterning apparatus, an image formed by the digital micromirror device is distorted due to lens aberration and error in assembling lens of an optical system mounted on the patterning head with the digital micromirror device, and thus position displacement of spots occurs at the time of the multiple exposure.
FIGS. 18A to 18D are schematic diagrams illustrating the position displacement of spots at the time of the multiple exposure, which can occur in the direct patterning apparatus using the digital micromirror device. In FIGS. 18A to 18D, each white circle denotes the corresponding irradiation spot formed on the object substrate by each micromirror. In an ideal case where there is no lens aberration, no error in assembling the lens, or the like of the optical system mounted on the patterning head of the direct patterning apparatus, the distortion does not occur in the image on the surface of the object substrate, and the irradiation spots are formed at the regular interval on the same scanning lines L by the micromirrors, as shown in FIG. 18A. However, as described above, the lens aberration, the error in assembling the lens, or the like practically occurs in the optical system. Consequently, as shown in FIGS. 18B to 18D, the distortion occurs in the image on the surface of the object substrate, and thus position displacements of the irradiation spots formed by the micromirrors occur. Likewise, due to the position displacements of the irradiation spots formed by the micromirrors, the interval between the irradiation spots on the same scanning lines L formed by the micromirrors becomes irregular. Since the optical system is individually mounted on each patterning head, the position displacement of the irradiation spot formed by the micromirrors becomes different for every patterning head, that is, every digital micromirror device. Consequently, an exposure amount (that is, an accumulated amount of irradiation of light) in one irradiation spot obtained by the multiple exposure by the plurality of micromirrors is different for every digital micromirror device as shown in FIGS. 18B to 18D.
FIG. 19 is a diagram illustrating one example of irradiance distribution of light by the digital micromirror devices in the direct patterning apparatus. As shown in the drawing, three digital micromirror devices D1, D2, and D3 are aligned in a direction nearly perpendicular to the relative moving direction of the object substrate (indicated by a thick arrow in the drawing). In the drawing, white circles and black circles each represent the micromirrors aligned two-dimensionally in the digital micromirror devices. Each of the digital micromirror devices D1, D2, and D3 is mounted on each patterning head of the direct patterning apparatus, so that the rows (or columns) of the micromirrors aligned two-dimensionally are tilted for a predetermined angle with respect to the relative moving direction of the object substrate.
Black circles shown in FIG. 19 denote the micromirrors positioned in the vicinity of joint portions (hereinafter, referred to as “stitch portions”) of alignment planes of the micromirrors of the digital micromirror devices D1, D2, and D3. Irradiance of light at the stitch portions of the digital micromirror device is reduced due to the lens aberration, the error in assembling the lens, or the like described in by referring to FIGS. 18B to 18D, compared to the vicinity of the center of the digital micromirror device. The exposure irregularity occurs on the object substrate due to the irregularity of the irradiance distribution of light.
FIG. 20 is a diagram illustrating a relationship between the exposure irregularity and defective resolution of the direct patterning apparatus using the digital micromirror devices. As shown in the drawing, three digital micromirror devices D1, D2, and D3 are aligned in a direction nearly perpendicular to the relative moving direction (indicated by a thick arrow in the drawing) of an object substrate P. In the drawing, the white circles and the black circles respectively represent the micromirrors aligned two-dimensionally in the digital micromirror devices, and the black circles especially represent the micromirrors existing in the vicinity of the stitch portions of the digital micromirror devices D1, D2, and D3.
As one example, a case will be described where pieces Q1 to Q8 to be semiconductor packages are attached on the surface of the object substrate P, and a wiring pattern is formed on each piece. In addition, there are areas (indicated by chain lines in the drawing) in which high-density wiring patterns are formed on the respective pieces Q1 to Q8. Hereinafter, in particular, the areas in which the high-density wiring patterns are formed are referred to as “minute pattern areas.”
As the digital micromirror devices D1, D2, and D3 expose the object substrate P which moves relatively with respect to the digital micromirror devices D1, D2, and D3 in a positional relationship shown in FIG. 20, each micromirror positioned in the vicinity of the centers of the digital micromirror devices exposes areas R1, R2, and R3 on the object substrate P, and each micromirror positioned in the vicinity of the stitch portions of the digital micromirrors expose areas T1 and T2. When the micromirror positioned in the vicinity of the stitch portions of the digital micromirror devices, which causes the exposure irregularity, exposes the minute pattern area (indicated by the shaded area) (areas T1 and T2), the defective resolution occurs in the corresponding area.
In order to remove the exposure irregularity causing the defective resolution, it can be considered that the optical system in high accuracy is used or the mounting position of the patterning head is finely adjusted with high precision. However, it requires lots of time, labors and costs in the work of assembling or adjusting the direct patterning apparatus.